Forest ThreatNet

Southern Research Station scientists and colleagues recently studied global patterns of non-native plant invasions, finding striking patterns on both continents and islands. Although invasive species numbers generally declined with increasing latitude, the highest alien species numbers occurred at the same latitude in both hemispheres, around 40 degrees. The pattern of decreasing invasion levels towards higher latitudes was also found on islands, whereas on continents a ‘humped’ pattern of increase-then-decline was observed. Overall, islands showed significantly higher invasion levels in continental regions. However, islands showed more variability in invasion levels on islands at low latitudes nearer the equator. In continental regions, only the mid-latitudes had high variability with both low and high invasion levels. 

In addition to latitude, people are a dominant factor explaining the observed patterns in plant invasion levels—but species pool size, climate warming, and biotic resistance likely also play a role. 

The scientists identified latitudes with invasion hotspots where management is urgently needed, and latitudes with many areas of low invasions but high conservation potential where prevention of future invasions should be the priority. Future work should closely monitor species invasions across latitudes and major geographic regions, and should focus on local-regional-global links with long-term perspectives. Learn more about this research here.

Pictured: Like many other invasive plant species in the southeastern United States, Kudzu (Pueraria montana) is an example of a poleward (in this case, northward) spreading invasive species. USDA Forest Service image.